Ultra-wideband, free space optical communication apparatus

ABSTRACT

Devices, systems, and methods for providing wireless personal area networks (PANs) and local area networks (LANs) using visible and near-visible optical spectrum. Various constructions and material selections are provided herein. According to one embodiment, a free space optical (FSO) communication apparatus includes a digital data port, an array of light-emitting diodes (LEDs) each configured to have a transient response time of less than 500 picoseconds (ps), and current drive circuitry coupled between the digital data port and the array of LEDs.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/889,844 entitled “ULTRA-WIDEBAND, FREE SPACE OPTICAL COMMUNICATIONAPPARATUS” (Attorney Docket No. 580/3/3/4 UTIL) which was filed on Jun.2, 2020, which is a continuation of U.S. patent application Ser. No.16/658,242 entitled “ULTRA-WIDEBAND, FREE SPACE OPTICAL COMMUNICATIONAPPARATUS” (Attorney Docket No. 580/3/3/3 UTIL) which was filed on Oct.21, 2019, which is a continuation of U.S. patent application Ser. No.16/379,841 entitled “ULTRA-WIDEBAND, FREE SPACE OPTICAL COMMUNICATIONAPPARATUS” (Attorney Docket No. 580/3/3/2 UTIL) which was filed on Apr.10, 2019, which is a continuation of U.S. patent application Ser. No.15/862,959 entitled “ULTRA-WIDEBAND, FREE SPACE OPTICAL COMMUNICATIONAPPARATUS” (Attorney Docket No. 580/3/3 UTIL) which was filed on Jan. 5,2018, which is a continuation of PCT Patent Application No.PCT/US2017/016916 entitled “ULTRA-WIDEBAND, WIRELESS OPTICAL HIGH SPEEDCOMMUNICATION DEVICES AND SYSTEMS,” (Attorney Docket No. 580/3 PCT)which was filed on Feb. 8, 2017, which claims benefit of and priority toU.S. Provisional Patent Application No. 62/293,291 entitled“ULTRA-WIDEBAND, WIRELESS OPTICAL HIGH SPEED COMMUNICATION DEVICES ANDSYSTEMS,” (Attorney Docket No. 580/3 PROV) which was filed on Feb. 9,2016, the contents of all of which are incorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to free-space optical (FSO) communication. Morespecifically, the disclosure relates to devices, systems, and methodsfor providing wireless high speed communication within personal areanetworks (PANs) and local area networks (LANs) using visible and nearvisible spectrum light emitting diodes (LEDs) and optical detectors.

BACKGROUND

Mobile devices equipped with high-resolution cameras and displays arecapable of capturing large volumes of multimedia content that can bestored locally on the mobile device. However, transferring and sharingof such content real-time among devices and servers require short-rangeconnectivity modems capable of delivering speeds of 20 gigabits persecond (Gbps) or higher. The dilemma for the mobile industry is that thecapability of radio technologies for wireless modems such as WirelessLocal Area Network (WLAN) are not keeping up with the exponential growthof multimedia content capabilities of mobile devices.

Without compression of the multimedia content, wired connectivity viacables is the only way to transfer the large amount of data amongdevices or between a device and the cloud. Currently the wired cableHigh-Definition Multimedia Interface (HDMI) 2.0b specification providesup to 18 Gbps of bandwidth and will support 4K Ultra High Definition(UHD) at 3480×2160 pixels per frame and 60 frames per second (fps) ofvideo content. The upcoming HDMI 2.1 specification will provide up to 48Gbps of bandwidth and will support 8K UHD at 7680×4320 pixels and 60 fpsof video content. The HDMI 2.1 specification will also provide supportfor 4K UHD at 120 fps.

High throughput WLAN IEEE standards, such as 802.11ac and 802.11ad, havebeen introduced to increase WLAN throughput. However, these standardsare still no adequate to meet the throughput demands of uncompressed 4Kand 8k UHD. IEEE 802.11ac has a maximum theoretical transfer rate 1.3Gbps. IEEE 802.11ac Wave 2 has a maximum theoretical transfer rate 2.34Gbps. IEEE 802.11ad has a maximum theoretical transfer rate of 7 Gbps.These current standards will not support uncompressed 4K and 8K UHDvideo transfer. Lossy compression such as h.264 or h.265 is typicallyused to reduce the needed bit rate.

The data throughput of radio transceivers is inherently limited by theavailability of commercial radio spectrum and their limited tuningrange. For example, in IEEE802.11ac standard, the channel bandwidths arespecified at either 80 MHz or 160 MHz in the 5 GHz ISM band. Withchannel bonding, WLAN 802.11ac transceivers have been operated at speedsof 866 Mbps. A single user operating at such speeds will use up theentire bandwidth of the local network! The next-generation of 802.11acutilizes Mu-MIMO feature (Multi-user, Multi-Input, Multi-Output) usingsmart antenna technology to focus dedicated radio beams on individualusers thereby increasing total bandwidth through spatial diversity.Mu-MIMO is expected to deliver up to 1.7 Gbps using a 4×4 MIMOconfiguration.

The IEEE802.11ad standard (WiGig™) takes advantage of higher spectrumavailability in the 57-64 GHz band (V-band). With about 7 GHz spectrumavailable, speeds of 5 Gbps have been demonstrated and potential speedsof 7 Gbps using multi-carrier OFDM modulation are being pursued.Millimeter-wave radio transceivers have significant complexity and costassociated therewith and suffer from multi-path and other channelimpairments in an indoor operation. Additionally, due to excessiveatmospheric absorption at V-band, the transmission range of WLAN802.11ad modems is limited between 2 and 3 meters even with complexantenna beam forming feature. While 802.11ad modems are being introducedto market, the industry is continuously looking for higher bandwidthwireless modems for next-generation devices.

Transmission in the optical region of the spectrum offers distinctadvantages over radio waves for wireless communications. The much highercarrier frequency in the optical range enables much higher modulationbandwidth. Atmospheric absorption in the optical region between infrared(IR) and ultraviolet (UV) can be much lower than that in the mm-wave andTerahertz (THz) frequencies depending on the choice of opticalwavelengths. This improves the communication range of optical wirelessmodem and reduces power consumption of the transmitter. Availabletransmit source power from microwave and mm-wave solid-state devicesdeclines with increasing carrier frequency as 1/f². Even with recentdevelopments in GaN power transistor technology, achieving power levelof 1 W at the Terahertz frequencies in high volume is not practical.Wireless 802.11ad modems are designed to operate at a range of 2 to 3meters with 10 mW transmitted power level in the V-band using CMOS andSiGe BiCMOS power amplifiers. In the future, even if additional radiospectrum is made available at higher frequency bands (e.g. Terahertzbands), radio modems face increasing atmospheric attenuation and loweravailable transmit power. In contrast, due to recent developments in GaNand GaAs based LED and laser technologies, optical power levels havebeen steadily increasing. CREE has demonstrated GaN LEDs with 300 lumensoptical output power per watt of dissipated power. Single-die LED arrayswith 18,000 lumens are commercially available today. Unlike radiocommunication, optical wireless links do not require licenses to operatein the visible or nearly-visible spectrum enabling OEMs to get productsfaster to market.

While lasers can be used as optical sources for the transceiver moduledisclosed, lasers require precise line-of-sight alignment with thedetector, which is not practical for mobile devices in typical consumeruse-cases. Defocusing of lasers can increase projection angle for thetransmitter, but it requires expensive optics, packaging and assemblyprocesses. LEDs, on the other hand, can operate over a wide projectionangles and can be operated in a point-to-multipoint networkconfiguration (e.g. wireless optical network in a room).

Multi-color LEDs can be employed at relatively low cost to createwavelength diversity in the optical link, thereby multiplying the datathroughput of the link. Disclosed herein are multi-wavelength LEDs todemonstrate full-duplex (simultaneous uplink and downlink) opticalcommunication. Multi-wavelength LED transmitters also offer the optionof wavelength modulation which provides more immunity to ambientinterferences and a more robust link. TABLE 1 summarizes thecommercially available LED technologies, their associated wavelength,built-in voltage and the semiconductor materials on which they arefabricated.

TABLE 1 Wavelength Voltage Color [nm] [ΔV] Semiconductor materialInfrared λ > 760 ΔV < 1.63 GaAs, AlGaAs Red 610 < λ < 760 1.63 < ΔV <2.03 AlGaAs, GaAsP, AlGaInP, GaP Orange 590 < λ < 610 2.03 < ΔV < 2.10GaAsP, AlGaInP, GaP Yellow 570 < λ < 590 2.10 < ΔV < 2.18 GaAsP,AlGaInP, GaP Green 500 < λ < 570 1.9 < ΔV < 4.0 GaP, AlGaInP, AlGaP,InGaN/GaN Blue 450 < λ < 500 2.48 < ΔV < 3.7  ZnSe, InGaN on SiCsubstrate Violet 400 < λ < 450 2.76 < ΔV < 4.0  InGaN on SiC substrateUltra- λ < 400 3.1 < ΔV < 4.4 Diamond (235 nm), violet AlGaN, AlN (210nm) White Broad ΔV = 3.5 Blue/UV diode with yellow spectrum phosphorous

Another important design factor for achieving high speed opticaltransmitters and receivers is how individual LEDs and detectors arescaled to achieve the desired signal levels. Bright LEDs aremanufactured today in the form of arrays of smaller LEDs on a single forthermal management reasons. A typical LED chip can consist of 8×8 or16×16 LED arrays. In today's LED bulbs, these arrays of micro-LEDs arepowered together to achieve the desired brightness. The individualmicro-LEDs in the array can be independently driven as individualtransmitters to form MIMO (multi-input, multi-output) spatial diversityfor the link, which further increase data throughput. MIMO is often usedin radio wireless transceivers to deal with multi-path interference andfading in the channel. However, MIMO technique requires much highercomplexity at the transmitter and receiver (CCD or CMOS photo sensor)thereby considerably increasing the cost of the system.

The micro-LEDs in today's LED arrays are designed for static DirectCurrent (DC) operation and are not suitable for high-frequencyoperation. Typical dimensions of a micro-LED and detectors may be on theorder of 50-100 μm on a side. At these dimensions, the resistivecapacitive (RC) time constant of the device is too high and uniform ACoperation of the entire diode active area cannot be achieved due tospreading resistance of the anode and cathode contacts.

The substrates of choice for most high-volume LEDs are either GaAs orSiC. Both material technologies lend themselves well for microwave andultra high-speed circuit implementations due to their semi-insulatingcharacteristics. In fact, GaAs and SiC/GaN materials today form thebackbone of microwave and millimeter-wave IC's for commercial andmilitary applications. Global Communications Semiconductor (GCS)Incorporated offers commercially available GaAs and SiC/GaN based LEDprocesses for product implementations.

Ultra High-Speed, Short-Range Connectivity for Mobile Devices

According to International Data Corporation (IDC), Worldwide QuarterlyMobile Phone Tracker, worldwide smart phone shipments was estimated at1.2 B units in 2014 and expected to reach 1.8 B units in 2018, resultingin a 12.3% compounded annual growth rate (CAGR) from 2013-2018. IDC alsoreports 245M units of tablet shipments in 2014. The majority of thesephones and tablets will be equipped with high-resolution displays andcameras and can be potential candidates for ultra-high-speed, wirelessoptical links. In addition to smart phone and tablets, other mobiledevices such as high-resolution digital cameras and camcorders, notebookcomputers and portable disk drives currently using USB (Universal SerialBus) as well as fixed devices such digital TV's, projectors. Additionaldevelopment of wireless optical dongles capable of replacing USB3 dataand HDMI2.0 (4K) video cables may be provided. Wireless optical modulesfor embedded applications in a wide range of electronic devices such asbut not limited to a smart watch, a smart phone, a tablet, a laptop, adigital camera, a digital camcorder, a computer monitor, a TV, aprojector, and a wireless access point may be provided. The overalladdressable market size for ultra-wideband wireless optical transceiverscan be well in excess of 2 B units by 2018. The adoption and attach rateof wireless optical transceivers to mobile devices should follow similartrend as WLAN modems integration into mobile devices. Based onpreliminary analysis, the cost of the wireless, optical transceiver willbe less than 802.11ad mm-Wave radio modems while its performance will besignificantly higher.

Indoor Wireless Networking for Home and Enterprise Applications

There is growing interest in using LEDs for in-building wirelessnetworking and location-based services. The LiFi™ Consortium wasestablished November 2011 to enable Giga-speed visible lightcommunication (VLC) applications. The Infrared Data Association (IrDA)(www.irda.org) also announced in 2011 working groups for thestandardization of 5 Gbps and 10 Gbps IrDA using IR sources while suchproducts have not reached the market yet.

There is an active worldwide effort to develop standards for VLC. TheIEEE802.15.7 WPAN (Wireless Personal Area Network) Task Group 7 hascompleted MAC and PHY layers specifications for VLC. The JapanElectronics and Information Technology Industries Association hasreleased the JEITA CP-1221 standard for VLC systems. While thestandardization activities have focused on the physical layer andapplication layer of VLC systems, the fundamental speed limitations ofVLC transceivers remains the main, stumbling block to the realization ofpractical, ultra-speed VLC transceiver.

There is also growing interest in using VLC for indoor enterpriseapplications. Philips has announced the Shopping Assistant applicationusing LED-based communication with mobile devices. In this application,the consumer can download information about each product as they browsethe store.

Smart Lighting for Automotive Transportation

Another potential market for LED-based VLCs is the automotivetransportation market. LED lighting due to their superior brightness andpower consumption is becoming the technology of choice for automobileheadlights, taillights, streetlights and traffic signaling. Smart LEDarray technology offers auto manufacturers the ability to incorporatenew functionality in the external and internal lighting ofnext-generation automobiles. VLC offers auto manufacturers potential ofauto-to-auto, and auto-to-streetlight and auto-to-traffic lightcommunications. This generates enormous potential for new applicationsin auto transportation. For example, auto-to-street headlight VLC canenable in-car wireless hot spots that can be used to access theInternet. Also, traffic lights can warn incoming cars aboutcross-section traffic and improve safety. Cars facing obstacles can warnseveral cars behind them to slow down and avoid potential accidents.

Another arena for WOC is the application of ultra-high-speed LEDtransceivers for 100 Gbps Ethernet backplanes for data centerapplications. With the enormous growth of cloud-based services andcomputing driven by social multi-media, the cost and power consumptionof 100 Gbpes Ethernet connections is becoming a major concern. Today'sEthernet cards employ copper connectivity using 10Gbase-T transceivers,which incur significant power consumption to drive copper cables at 10Gbps over distances of several meters. Ultra-high-speed LED transceiverscombined with low-cost multi-mode fibers can significantly reduce thepower consumption of Ethernet links in this application.

There are other applications of optical wireless applications such assecure communications for mobile financial transactions but there isgrowing adoption of Near Field Communications (NFC) technology in mobiledevices. Ultra-high-speed, wireless optical communication has militaryapplications as well. For examples, reconnaissance Unmanned Air Systems(UAS) (or drones) acquire large amounts of imagery data and sensorinformation, which are downloaded directly to ground or throughsatellite via radio links. The radio links have bandwidth limitationsand subject to interference and eavesdropping. Optical wireless linkscan offer a more secure air-to-ground, ultra-high-speed link to download UAS information to ground terminals. There has been demonstrated 1Gbps video stream downlink from an aircraft moving at an altitude of 7km and speed of 800 km/h. Lasers were used as the optical source withcomplex alignment mechanics for the laser and the ground-based terminal.The solutions disclosed herein can eliminate the need for complexline-of-sight alignment systems that are required for laser free-spaceoptical systems. While this system is designed for specific militaryapplication, it has potential applications to the commercial UAS marketand demonstrates the viability of ultra-wideband optical, wirelesscommunication over large distances.

While the potential market for LED-based ultra-high-speed wirelesscommunication is substantial, innovative approaches are required todevelop and build ultra-high-speed LED transceivers. The “white” LEDdevice design and optimization have been driven by the industry toachieve the lowest cost and power consumption for a target level ofbrightness. No considerations have been given to the switching speed ofLEDs for communication applications. While attempts have been made touse off-the-shelf LEDs for wireless optical communications, suchattempts have had little success due to intrinsic speed limitation ofthe micro-LEDs and detectors.

SUMMARY

Disclosed herein are devices, systems, and methods for providingwireless personal area networks (PANs) and local area networks (LANs)using visible and near-visible optical spectrum. Various constructionsand material selections are provided herein.

According to one embodiment, a light-emitting diode (LED) includes asubstrate, a carrier confinement (CC) region positioned over thesubstrate, and an active region position over the CC region. The CCregion includes a first CC layer comprising indium gallium phosphide anda second CC layer position over the first CC layer. The second CC layerincludes gallium arsenide phosphide. The active region is configured tohave a transient response time of less than 500 picoseconds (ps)

The LED may have a quantum well structure or a multi quantum wellstructure. The active region may include indium gallium arsenide and mayhave an indium composition between 10% and 35%. The active region of theLED may have a thickness between 50 and 150 angstroms.

A first barrier layer may be positioned between the CC region and theactive region. The first barrier layer may have a phosphorouscomposition between 25% and 80%. The first barrier layer may have athickness between 25 and 75 angstroms A second barrier layer may bepositioned over the active region. The second barrier layer may have aphosphorous composition between 40% and 50%. The second barrier layermay have a thickness between 30 and 40 angstroms.

The LED may include an n-type contact layer positioned between thesubstrate and the CC region; and a p-type contact layer positioned overthe second barrier layer. The first CC layer may have an indiumcomposition between 45% and 55%, and the second CC layer has aphosphorous composition between 25% and 80%. The first CC layer may havea thickness between 100 and 2000 angstroms and the second CC layer has athickness between 25 and 75 angstroms.

The CC region may include a third CC layer positioned over the second CClayer. The third CC layer may include indium gallium phosphide. A fourthCC layer may be positioned over the third CC layer. The fourth CC layermay include gallium arsenide phosphide. The third CC layer may have anindium composition between 45% and 55%, and the fourth CC layer may havea phosphorous composition between 25% and 80

The CC region may include a fifth CC layer positioned over the fourth CClayer. The fifth CC layer may include indium gallium phosphide. A sixthCC layer may be positioned over the fifth CC layer. The sixth CC layermay include gallium arsenide phosphide.

In other embodiments, the third CC layer and the fifth CC layer may eachhave an indium composition between 45% and 55% and the fourth CC layerand the sixth CC layer each have a phosphorous composition between 25%and 80%.

In other embodiments the first CC layer, the second CC layer, the thirdCC layer, the fourth CC layer, the fifth CC layer, and the sixth CClayer each have a thickness between 25 and 150 angstroms.

The n-type contact layer and the p-type contact layer may each includegallium arsenide. The n-type contact layer may have a thickness between5000 and 20000 angstroms and the p-type contact layer may have athickness between 500 and 5000 angstroms.

According to another embodiment, a method of forming the LED includesproviding an epitaxial structure on a substrate. The epitaxial structureincludes a substrate, a carrier confinement (CC) region positioned overthe substrate, and an active region position over the CC region. The CCregion includes a first CC layer comprising indium gallium phosphide anda second CC layer position over the first CC layer. The second CC layerincludes gallium arsenide phosphide. The active region is configured tohave a transient response time of less than 500 picoseconds (ps).

According to another embodiment a free space optical (FSO) communicationapparatus includes a digital data port and an array of LEDs. Each LEDconfigured to have a transient response time of less than 500 ps, andcurrent drive circuitry coupled between the digital data port and thearray of LEDs.

The digital data port may include an audio/video interface. Theaudio/video interface may be configured for uncompressed video. Thedigital data port may be a High-Definition Multimedia Interface (HDMI)port, a DisplayPort interface port or a Digital Visual Interface (DVI)port. The digital data port may be a Universal Serial Bus (USB) port, aSerial ATA (SATA) interface port, or an Ethernet port. In otherembodiments, the digital data port may be an optical data port. Thedigital data port may be a gigabit interface converter (GBIC) interfaceport, a small form-factor pluggable (SFP) interface port or a 10 GigabitSmall Form Factor Pluggable (XFP) interface port.

The FSO communication apparatus may include a Wilkinson power dividercoupled between the digital data port and the current drive circuitry.In other embodiments, a traveling way array may be coupled between thedigital data port and the current drive circuitry.

In other embodiments, each LED of the array of LEDs may include asubstrate, a carrier confinement (CC) region positioned over thesubstrate, and an active region position over the CC region. The CCregion may include a first CC layer comprising indium gallium phosphideand a second CC layer position over the first CC layer. The second CClayer may include gallium arsenide phosphide. Each LED may include anactive region over the CC region;

In other embodiments, the FSO communication apparatus also includes anarray of optical detectors, wherein each optical detector is configuredto have a bandwidth of a least 10 gigahertz (GHz); and transimpedanceamplifier circuitry coupled between the digital data port and the arrayof optical detectors.

The FSO communication apparatus may also include a Wilkinson powercombiner coupled between the digital data port and the transimpedanceamplifier circuitry. In other embodiments, the FSO communicationapparatus may also include a travelling wave array coupled between thedigital data port and the transimpedance amplifier circuitry.

The FSO communication apparatus may be implemented in at least one of asmart watch, a smart watch, a smart phone, a tablet, a laptop, a digitalcamera, a digital camcorder, a computer monitor, a TV, a projector, anda wireless access point.

According to another embodiment, an LED includes a substrate and a CCregion positioned over the substrate. The CC region includes a first CClayer. The first CC layer includes aluminum gallium arsenide. The CCregion includes a second CC layer positioned over the first CC layer.The second CC layer also includes aluminum gallium arsenide. The LEDalso includes an active region positioned over the CC region. The activeregion is configured to have a transient response time of less than 500ps. The LED also includes an electron blocking layer (EBL) positionedover the active region. The EBL includes aluminum gallium arsenide.

The LED may have a quantum well structure or a multi quantum wellstructure. The active region may include gallium arsenide and may have athickness between 50 and 150 angstroms. The LED may also include a firstbarrier layer positioned between the CC region and the active region;and a second barrier layer positioned over the active region. The firstbarrier layer has an aluminum composition between 25% and 45%. The firstbarrier layer may have a thickness between 25 and 75 angstroms. The LEDmay also include an n-type contact layer positioned between thesubstrate and the CC region, and a p-type contact layer positioned overthe second barrier layer.

In other embodiments, the first and second CC layers may each have analuminum composition between 25% and 45%. The first CC layer may have athickness between 100 and 2000 angstroms, and the second CC layer mayhave a thickness between 25 and 75 angstroms. The EBL may have analuminum composition between 25% and 45%, and may have a thicknessbetween 100 and 2000 angstroms. The n-type contact layer and the p-typecontact layer may each include gallium arsenide. The n-type contactlayer may have a thickness between 5000 and 20000 angstroms, and thep-type contact layer may have a thickness between 500 and 5000angstroms.

According to another embodiment, a method of forming an LED includesproviding an epitaxial structure on a substrate. The epitaxial structureincludes a CC region positioned over the substrate. The CC regionincludes a first CC layer comprising aluminum gallium arsenide and asecond CC layer positioned over the first CC layer. The second CC layeralso includes aluminum gallium arsenide. The epitaxial structure alsoincludes an active region positioned over the CC region. The activeregion is configured to have a transient response time of less than 500ps. The epitaxial structure also includes an electron blocking layer(EBL) positioned over the active region. The EBL includes aluminumgallium arsenide.

According to another embodiment, an LED includes a substrate and a CCregion positioned over the substrate. The CC region includes a first CClayer. The first CC layer includes aluminum gallium nitride. The CCregion includes a second CC layer positioned over the first CC layer.The second CC layer also includes aluminum gallium nitride. The LEDincludes an active region positioned over the CC region. The activeregion is configured to have a transient response time of less than 500ps.

The active region may be configured as a quantum well structure or amulti quantum well structure. The active region may include indiumgallium nitride and may have an indium composition between 0 and 45%.The active region may have a thickness between 50 and 150 angstroms. TheLED may also include a first barrier layer positioned between the CCregion and the active region; and a second barrier layer position overthe active region. The first barrier layer may have aluminum compositionbetween 0% and 45%, and may have a thickness between 25 and 75angstroms. The LED may also include an n-type contact layer positionedbetween the substrate and the CC region, and a p-type contact layerpositioned over the second barrier layer.

In other embodiments, the first and second CC layers may each have analuminum composition between 10% and 45%. The first CC layer may have athickness between 100 and 2000 angstroms and the second CC layer mayhave a thickness between 25 and 75 angstroms. The n-type contact layerand the p-type contact layer may each include gallium nitride. Then-type contact layer may have a thickness between 5000 and 20000angstroms; and The p-type contact layer may have a thickness between 500and 5000 angstroms.

According to another embodiment, a method of forming an LED includesproviding an epitaxial structure on a substrate. The epitaxial structureincludes a CC region positioned over the substrate. The CC regionincludes a first CC layer. The first CC layer includes aluminum galliumnitride. The CC region includes a second CC layer positioned over thefirst CC layer. The second CC layer also includes aluminum galliumnitride. The epitaxial structure includes an active region positionedover the CC region. The active region is configured to have a transientresponse time of less than 500 picoseconds (ps).

In another embodiment, an LED includes a substrate and a CC regionpositioned over the substrate. The CC region includes a first CC layer.The first CC layer includes aluminum gallium antimonide. The CC regionalso includes a second CC layer positioned over the first CC layer. Thesecond CC layer also includes aluminum gallium antimonide. The LEDincludes an active region positioned over the CC region, the activeregion is configured to have a transient response time of less than 500ps. The LED also includes an EBL positioned over the active region. TheEBL includes aluminum gallium antimonide.

The active region may be configured as a quantum well structure or amulti quantum well structure. The active region comprises indium galliumantimonide and may have an indium composition between 10 and 45%. Theactive region may have a thickness between 50 and 150 angstroms. The LEDmay include a first barrier layer positioned between the CC region andthe active region, and a second barrier layer positioned over the activeregion. The first barrier layer may have an aluminum composition between20% and 45%, and may have a thickness between 25 and 75 angstroms. TheLED may also include an n-type contact layer positioned between thesubstrate and the CC region, and a p-type contact layer positioned overthe second barrier layer.

In other embodiments, the first and second CC layers may each have analuminum composition between 10% and 45%. The first CC layer may have athickness between 100 and 2000 angstroms and the second CC layer mayhave a thickness between 25 and 75 angstroms.

The EBL may have an aluminum composition between 10% and 45% and mayhave a thickness between 100 and 2000 angstroms. The n-type contactlayer and the p-type contact layer each comprise gallium antimonide. Then-type contact layer may have a thickness between 5000 and 20000angstroms, and the p-type contact layer may have a thickness between 500and 5000 angstroms.

According to another embodiment, a method of forming a LED includesproviding an epitaxial structure on a substrate. The epitaxial structureincludes a CC region positioned over the substrate, the CC regiondefines a first CC layer comprising aluminum gallium antimonide; and asecond CC layer positioned on the first CC layer. The second CC layerincludes aluminum gallium antimonide. The epitaxial structure alsoincludes an active region positioned over the CC region. The activeregion is configured to have a transient response time of less than 500ps. The epitaxial structure also includes an EBL positioned over theactive region. The EBL includes aluminum gallium antimonide.

BRIEF DESCRIPTION OF THE DRAWINGS

The present embodiments are illustrated by way of example and are notintended to be limited by the figures of the accompanying drawings. Inthe drawings:

FIG. 1 depicts a block diagram illustrating an example of acommunication link including two optical wireless transceiver modules.

FIG. 2 depicts a block diagram of the communication link with twodual-wavelength, optical wireless transceiver modules.

FIG. 3 depicts a Point-to-Multipoint, networked operation of wirelessoptical transceivers using multiple-wavelengths.

FIG. 4 depicts a schematic of the disclosed “In-Phase Optical LED &Detector Arrays” for ultra-wideband wireless optical applications.

FIG. 5 depicts a schematic of a Travelling Wave LED and Detector Array,Wireless Optical Transceiver.

FIG. 6 depicts an equivalent circuit model of an LED/Detector pair in awireless optical transceiver.

FIG. 7 depicts an electrical equivalent circuit model for the TravellingWave Wireless Optical Transceiver of FIG. 5 and assuming N=4.

FIG. 8 depicts an electrical simulation of the disclosed opticalwireless link.

FIG. 9 depicts an ultra-high speed single/multi quantum well(s) GaAsbased LED structure with Carrier Confinement Layer.

FIG. 10 depicts an ultra-high speed single QW LED structure withalternate six layers of GaAsP and InGaP acting as a carrier confinementlayer (CCL).

FIG. 11 depicts an ultra-high speed single QW LED structure withalternate four layers of GaAsP and InGaP acting as carrier confinementlayer (CCL).

FIG. 12 depicts an ultra-high speed single QW LED structure with twolayers of GaAsP and InGaP acting as a carrier confinement layer (CCL).

FIG. 13 depicts a comparison of the luminous output power and efficiencyof the single QW InGaAs/GaAsP LEDs with different CCLs.

FIG. 14 depicts a 10 GHz transient response at 1.7 V of LED STR#3.

FIG. 15 depicts a 20 GHz transient response at 1.7 V of LED STR#3.

FIG. 16 depicts a DC luminous output power and efficiency of 1×1000μ2single QW InGaAs/GaAsP LED with 23% In composition in the QW and 45% Pin the barriers;

FIG. 17 depicts a 10 GHz transient response at 1.7 V of 1×1000μ2 singleQW InGaAs/GaAsP LED with 23% In composition in the QW and 45% P in thebarriers.

FIG. 18 depicts an emission spectrum of LED STR#3. Peak emissionwavelength is 998 nm.

FIG. 19 depicts a Y-component current spreading of 5μ LED with three p+electrode each of 0.7μ on top.

FIG. 20 depicts a Y-component current spreading of 5μ LED with three p+electrode each of 0.7μ embedded in the p+ layer.

FIG. 21 depicts Y-component current spreading of 5μ LED with five p+electrode each of 0.3μ on top.

FIG. 22 depicts a comparison of 10 GHz transient response at 1.7 V for5μ LEDs of different p+ electrode designs and the ideal structure (Idealp+ electrode across the entire device length).

FIG. 23 depicts a top view of the LED.

FIG. 24 depicts an example of thickness of the metal stacks of p+electrode—100 Å thick Titanium, 100 Å Platinum and 6800 Å Gold.

FIG. 25 depicts a comparison of the 10 GHz transient performance ofdevices of different widths and the ideal structure with a p+ electrodeacross the entire device width.

FIG. 26 depicts a planer LED structure two three p+ electrodes on topand two n+ electrodes.

FIG. 27 depicts a 20 GHz sinusoidal response at 1.7 V of the LEDstructure shown in FIG. 26.

FIG. 28 depicts an ultra-high speed single QW AlGaAs/GaAs LED structure.

FIG. 29 depicts a luminous output power and efficiency of a single QWAlGaAs/GaAs LED.

FIG. 30 depicts a 10 GHz transient response at 1.7 V of single QWAlGaAs/GaAs LED.

FIG. 31 depicts an emission spectra of single QW AlGaAS/GaAs LED.

FIG. 32 depicts a single QW InGaN/AlGaN ultra-high speed LED.

FIG. 33 depicts a luminous output power and efficiency of single QWInGaN/AlGaN LED.

FIG. 34 depicts a 10 GHz transient response at 3.5 V of single QWInGaN/AlGaN LED.

FIG. 35 depicts an emission spectra of single QW InGaN/AlGaN LED with11% Indium composition in the InGaN QW. The peak emission wavelength is0.4μ;

FIG. 36 depicts an example of single QW InGaN/AlGaN LED with 11% Indiumcomposition in the InGaN QW. The distance between the n+ electrodes fromthe mesa is 0.5μ.

FIG. 37 depicts a 20 GHz sinusoidal response at 3.5 V of single QWInGaN/AlGaN LED shown in FIG. 36.

FIG. 38 depicts an illustration of a flip-chip GaN LED.

FIG. 39 depicts an ultra-high bandwidth InGaSb/AlGaSb LED structure.

FIG. 40 depicts a luminous output power and efficiency of single QWInGaSb/AlGaSb LED.

FIG. 41 depicts a 10 GHz transient response at 0.8 V of single QWInGaSb/AlGaSb LED.

FIG. 42 depicts an emission spectra of single QW InGaSb/AlGaSb LED with25% Indium composition in the InGaSb QW. The peak emission wavelength is1.68μ.

FIG. 43 depicts a conduction band diagram of 10 QW InGaAs/GaAsPphotodetector at 2.7 V and 5 V reverse bias.

FIG. 44 depicts an ultra-high speed 4 QW GaAs based photodetectorstructure.

FIG. 45 depicts generated current versus wavelength of 4 QW InGaAs/GaAsPdetector of L=20μ at 2.7 V. The cutoff wavelength is 1.12 μm.

FIG. 46 depicts an ultra-high speed 4 QW InGaAs/GaAsP photodetector of10μ length with two p+ electrodes on top each of 1 μm.

FIG. 47 depicts an ultra-high speed 4 QW InGaAs/GaAsP photodetector of20μ length with two p+ electrodes on top each of 1 μm.

FIG. 48 depicts an ultra-high speed 4 QW InGaAs/GaAsP photodetector of50μ length with four p+ electrodes on top each of 1 μm.

FIG. 49 depicts a generated photo-current at 10 GHz transient responseat 2.7 V for single QW InGaAs/GaAsP photodetector of lengths 10μ, 20μand 50μ.

FIG. 50 depicts an ultra-high speed MQW InGaN/AlGaN photodetector.

FIG. 51 depicts an ultra-high speed MQW InGaSb/AlGaSb photodetector.

FIG. 52 depicts an LED and photodetector integrated in one device. P+terminal is common to both LED and detector.

FIG. 53 depicts an LED and photodetector integrated in one device. n+terminal is common to both LED and detector.

FIG. 54 depicts an emission spectrum of single QW InGaAs/GaAsP LED (23%In, 45% P in p-side barrier and 60% P in n-side barrier) at 1.6 V and1.9 V. The peak emission wavelength at 1.6 V is 1000 nm and at 1.9 V is903 nm.

FIG. 55 depicts a luminous power and efficiency of 5×1000μ2 single QWInGaAs/GaAsP LED (23% In, 45% P in p-side barrier and 60% P in n-sidebarrier). The output luminous power is 40 mW @ 1.6 V and 373 mW @1.9 V.The efficiency of the device is 79.8% @ 1.6 V and 72.8% @ 1.9 V.

FIG. 56 depicts an emission spectrum of single QW InGaAs/GaAsP LED (30%In, 60% P in p-side barrier and n-side barrier) at 1.6 V and 1.9 V. Thepeak emission wavelength at 1.6 V is 1112 nm and at 1.9 V is 968 nm.

FIG. 57 depicts a mission spectrum of single QW InGaAs/GaAsP LED (30%In, 45% P in the barriers) at 1.6 V and 1.8 V. The peak emissionwavelength at 1.6 V is 1070 nm and at 1.9 V is 917 nm.

FIG. 58 depicts a luminous power and efficiency of 1×1000μ2 single QWInGaAs/GaAsP LED (30% In in the QW, 45% P in the barriers). The outputluminous power is 22 mW @ 1.6 V and 65 mW @ 1.8 V. The efficiency of thedevice is 76.5% @ 1.6 V and 68.1% @ 1.8 V.

FIG. 59 depicts a 10 GHz transient response at 1.6 V and 1.8 V of singleQW InGaAs/GaAsP LED with 30% Indium in the QW and 45% P in the barriers.

FIG. 60 depicts a wavelength division multiplexing (WDM) system usingtwo LEDs and two photodetectors.

FIG. 61 depicts a full duplex (bi-directional) communication systemusing two LEDs and two photodetectors.

FIG. 62 depicts two LEDs emitting light at different frequenciesintegrated into one device. P+/P layers are common to both the LEDs. QW1and QW2 denote the active regions of the device.

FIG. 63 depicts two LEDs emitting light at different frequenciesintegrated into one device. n+/n layers are common to both the LEDs. QW1and QW2 denote the active regions of the device.

FIG. 64 depicts a photodetectors design scheme to detect signals of twodifferent wavelengths—‘λ1’ & ‘λ2’.

FIG. 65 depicts an absorption spectra of the photodetectors D1 and D2.Cutoff wavelengths of detector 1 and detector 2 are ‘λ1’ & ‘λ2’respectively.

FIG. 66 depicts three terminal photodetector with two sets of InGaAs QWsof different Indium composition.

FIG. 67 depicts an absorption spectrum of the three terminalphotodetector for incident light with peak emission wavelength of 1070nm. Maximum absorption occurs in the lower QWs with 23% Indiumcomposition.

FIG. 68 depicts an absorption spectrum of the three terminalphotodetector for incident light with peak emission wavelength of 917nm. Light absorption occurs in both the upper (10% Indium) and lower(23% Indium) QWs.

FIG. 69 depicts a transient response of the three terminal photodetectorfor incident light with peak emission wavelength of 1070 nm.

DETAILED DESCRIPTION

The following description and drawings are illustrative and are not tobe construed as limiting. Numerous specific details are described toprovide a thorough understanding of the disclosure. However, in certaininstances, well-known or conventional details are not described in orderto avoid obscuring the description. References to “one embodiment” or“an embodiment” in the present disclosure can be, but not necessarilyare, references to the same embodiment and such references mean at leastone of the embodiments.

Reference in this specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the disclosure. The appearances of the phrase “in one embodiment” invarious places in the specification are not necessarily all referring tothe same embodiment, nor are separate or alternative embodimentsmutually exclusive of other embodiments. Moreover, various features aredescribed which may be exhibited by some embodiments and not by others.Similarly, various requirements are described which may be requirementsfor some embodiments but not other embodiments.

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the disclosure, and in thespecific context where each term is used. Certain terms that are used todescribe the disclosure are discussed below, or elsewhere in thespecification, to provide additional guidance to the practitionerregarding the description of the disclosure. For convenience, certainterms may be highlighted, for example using italics and/or quotationmarks. The use of highlighting has no influence on the scope and meaningof a term; the scope and meaning of a term is the same, in the samecontext, whether or not it is highlighted. It will be appreciated thatsame thing can be said in more than one way.

Consequently, alternative language and synonyms may be used for any oneor more of the terms discussed herein, nor is any special significanceto be placed upon whether or not a term is elaborated or discussedherein. Synonyms for certain terms are provided. A recital of one ormore synonyms does not exclude the use of other synonyms. The use ofexamples anywhere in this specification, including examples of any termsdiscussed herein, is illustrative only, and is not intended to furtherlimit the scope and meaning of the disclosure or of any exemplifiedterm. Likewise, the disclosure is not limited to various embodimentsgiven in this specification.

Without intent to limit the scope of the disclosure, examples ofinstruments, apparatus, methods and their related results according tothe embodiments of the present disclosure are given below. Note thattitles or subtitles may be used in the examples for convenience of areader, which in no way should limit the scope of the disclosure. Unlessotherwise defined, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which this disclosure pertains. In the case of conflict, thepresent document, including definitions, will control.

Currently, LED devices on the market are developed for maximumbrightness under static DC conditions. The actual device area or cell onthe LEDs is optimized to conform to the thermal and reliabilityconstraints under DC bias conditions. Once the cell has been optimized,then an array of such cells are connected in parallel to achieve targetbrightness. For example, each micro-LED element of an 8×8 LED array mayhave an active area of 100×100 micrometers (μm²). At these dimensions,when a high-frequency signal is applied in conjunction with the DC biasto the micro-LED, the distributed RC effects (series contact resistanceR, and shunt junction capacitance C) are too high causing a large innerportion of the diode area to remain inactive. In other words, while theentire diode area receives the DC bias voltage, the high-frequency ACsignal is excessively attenuated as it travels to the center portion ofthe diode area. In effect, only the light from the peripheral region ofLED is modulated at the desired signal frequency with large percentageof the diode not responding to modulation signal (“the blind spot”). Asthe frequency is increased, the modulated area of the LED becomessmaller thus reducing the high-frequency, utilization factor of the LED.For a 100×100 μm2 micro-LED, the high-frequency “blind spot” could reach90% of the total LED area. Under these conditions, the “blind spot” actsas a large capacitor shunting the desired high frequency signal toground without producing modulated light.

Another key factor limiting the switching speed of LEDs forcommunication applications are the intrinsic “spontaneous emission” and“recombination” rates. These rates determine how fast electron-holepairs generate due to applied voltage can recombine in the LED togenerate optical power. This limitation is a property of the materialstructure of the LED quantum well.

Embodiments of the present disclosure include devices, systems, andmethods for providing personal area networks (PANs) and local areanetworks (LANs) using visible spectrum light emitting diodes (LEDs) andoptical detectors.

Disclosed are novel LED/detector transceivers are described that arecapable of transmitting and receiving data at greater than 20 Gbps. Thismay require: 1—Novel device layout and material structure for themicro-LED cell to achieve lowest RC time-constant without significantcompromise in the conversion efficiency of the LED array. 2—Novelhigh-frequency splitting/combining circuits that can distribute thehigh-frequency signal among the micro-LED cells in an array to achievein-phase operation of the entire LED array at the desired frequency.

Disclosed herein are ultra-wideband, wireless optical devices andtransceivers capable of breaking wireless data barriers and deliveringdata speeds in excess of 20 Gbps for consumer electronics, communicationinfrastructure and defense electronics markets. Such speeds are far inexcess of what is available on the market with radio modems and willsignificantly enhance communication among mobile devices. The disclosedtransceivers incorporate novel Light-Emitting Diodes (LEDs) andphoto-detectors driven by innovative high-frequency circuits to achievethe desired performance targets. Such structures may be implementedwithin a smart watch, a smart phone, a tablet, a laptop, a digitalcamera, a digital camcorder, a computer monitor, a TV, a projector, awireless access point, or any device associated with the Internet ofThings (IoT).

High Frequency Combining Circuits of Micro-LED and Detector Array

In order to achieve the total transmit power requirement for an opticalwireless link, it is often necessary to combine several LEDs and operatethem in unison. The same applies to the receiver side where the detectorcells have to be combined to increase conversion gain required for theoptical link budget. The electrical and optical combining of micro LEDand detector cells at high frequencies pose unique challenges as signaltraces interact with the internal device capacitances and resistances tocause phase shifts among micro LEDs in an array. This causes the microLEDs (and detectors) to not operate in phase thereby distorting thetransmitted signal. Therefore, circuit-level combining techniques haveto be employed to ensure the combined LED transmitter or detectorreceiver arrays can operate at very high bandwidths (switchingfrequencies) while maintain signal integrity. Improper combining of theLED cells in an array can cause the electrical-to-optical conversionefficiency to drop rapidly at high frequencies limiting the operationbandwidth of the transmitter. Disclosed herein are novel combiningcircuits for the LED and detector arrays to scale the LED optical powerand detector sensitivity while achieving ultra-wideband operationfrequency. Special design considerations are given to the design of DCbias circuitry to ensure minimal impact on the high-frequency operationof LEDs. The combining and dividing circuit are implemented on theLED/detector semi-insulating substrate to achieve best performance andlow assembly cost.

FIG. 1 illustrates a block diagram 100 of two optical transceivers 105 aand 105 b in a wireless link. In this configuration, both opticaltransceivers 105 a and 105 b operate on the same wavelength in atime-division, half-duplex mode (i.e. one side is in the transmit-onlymode while the other side is in the receive-only mode). Full-duplexcommunication with this approach is very difficult due to the receiverbeing blinded by its own transmitter signal. Half-duplex links issufficient for most consumer electronic communication applications asrarely, full-duplex (i.e. simultaneous and bi-directional) communicationat high-speed is required. Most often, data is transferred at highspeeds from one device to another.

While serial communication standards such as USB3 and HDMI havebi-directional modes, they can be mapped over a serial link in atime-division half-duplex mode similar to the IrDA (Infrared DataAssociation) standard. The primary transceiver controls the timing ofthe link while the secondary transceiver is in the receive mode.Bi-directional communication is achieved by switching the primary andsecondary roles of the transceiver during the communication. In theimplementation of FIG. 1, the LED and Detector devices can reside on thesame chip (substrate) or two different chips depending on the level ofreceiver sensitivity required. For short-range communication where highlevel of detector sensitivity is not required, the LED and detectorfunctions can be integrated on the same chip. For longer rangecommunication and enhanced receiver sensitivity, the detector may be ona separate chip whose material structure is optimized for the detector.

The optical transceivers 105 a and 105 b of FIG. 1 can also employwavelength diversity, (i.e. communication over multiple wavelengths).FIG. 2 illustrates a block diagram 200 of optical transceivers 205 a and205 b employing a two-wavelength optical receiver implementation. Inthis implementation, two LED/detector pairs operate simultaneously attwo different wavelengths. This configuration offers two distinctadvantages: First, the effective communication data rate can be doubledrelative to the single-wavelength case by transmitting two simultaneousdata streams from the transmitting module to the receiving module at twoseparate wavelengths. Second, full-duplex, wireless communication can beachieved by having both modules simultaneously transmit on one channeland receive on the second channel. While this approach may require morecomponents, it is a more robust solution which allows for full-duplexoperation of the link effectively doubling the communication speed.Disclosed herein are innovative devices capable of transmitting andreceiving multi-wavelength wireless optical signals at very high speeds.

The wavelength diversity in this product implementation can be extendedfurther to N wavelengths (i.e. one wavelength per channel). FIG. 3depicts a point-to-multipoint, networked diagram 300 of wireless opticaltransceivers 310 a-310 d using multiple-wavelengths. Each channel can beutilized to communicate an independent data stream. This configurationenables point-to-multipoint and peer-to-peer communication among anumber of devices. Such devices 310 a-310 d may each be one of a smartwatch, a smart phone, a tablet, a laptop, a digital camera, a digitalcamcorder, a computer monitor, a TV, a projector, and/or a wirelessaccess point.

In order to split and combine the signals from LEDs and detectorsefficiently at very high frequencies, and in-phase approach and atravelling wave approach disclosed.

LED and Detector Arrays with in-Phase Signal Divider and Combiners

FIG. 4 illustrates an electrical schematic 400 of a wireless opticaltransceiver where the transmitter consist of an array of micro-LEDsdriven by a Wilkinson in-phase dividing circuit including segments oftransmission lines of certain characteristic impedance and electricallengths. The length and impedance of each transmission line segmentdepends on the number of micro-LEDs in the circuit and can be optimizedto achieve in-phase operation of the micro-LEDs over wide bandwidth.This approach constitutes a “single-stage” dividing circuit where theinput impedance is transformed to the individual input impedance of eachmicro-LED. So, the dividing circuit serves as both impedance matching aswell as signal dividing circuit.

Similarly, on the receiver side, the photo current from individualmicro-detector cells are combined using in-phase networks which alsoserve as impedance matching networks to transform the detector impedanceto that required by a trans-impedance amplifier (TIA). This approach canbe expanded to multi-stage divider and combining circuits to furtherincrease the electrical bandwidth of the overall transceiver. In thisapproach, more than one divider network shown in FIG. 4 will be used incascade to step down the input impedance to the LED impedance inmultiple steps with the added benefit of increased bandwidth.

In addition to in-phase dividers and combiners, micro-LEDs can becombined out-phase in an array and then combined in a conjugate phasemanner on the receiver side. Referring again to FIG. 4, consider a4-element array in which the LED1, LED2, LED3, and LED4 are driven at 0,90, 180, and 270 phase angles (relative to LED1) and the opposingdetectors (DET1, DET2, DET3 and DET4) are combined at 270, 180, 90, and0 degrees. In this configuration, even though the individual LEDs aredriven orthogonally out of phase, the output combining will add thesignals from individual detectors in an orthogonal fashion toreconstitute the desired signal at the output.

Travelling Wave LED and Detector Arrays

FIG. 5 illustrates a schematic 500 of a travelling wave LED and detectorarray, wireless optical transceiver. This approach discloses combiningindividual micro-LEDs (and micro-detectors) in a travelling wave circuitstructure in which each micro-LED is driven by an electrical signal withprogressive phase (or time delay).

In this approach, the input transmission line segments combine with theindividual capacitance of the micro-LEDs to form a “travelling wave”transmission line structure. By selecting appropriate values of eachtransmission line characteristic impedance (Z) and electrical length(E), as well as those of the input and termination impedances, thebandwidth of the input circuit can be dramatically increased. FIG. 6illustrates schematics 600 of simplified electrical equivalent circuitmodels of an LED and photodetector in a wireless optical transceiver.

The input circuit represents the electrical model for the micro-LEDdiode. The output circuit shows the electrical model for thephoto-detector including the photo-current source and its parasiticcapacitances and resistances. The current source has a photo-currentgain and an associate time-delay which represents the time it takes forthe optical signal to travel from the LED to the detector. In order tosimulate the performance of the Travelling Wave Wireless Opticaltransceiver of FIG. 5, there is a need to account for opticaltransmission from each LED to each one of the detectors as shown by thedashed arrows in FIG. 5. In effect, the travelling wave circuit of FIG.5 represents a “Matrix Travelling Wave Optical Transceiver”. FIG. 7illustrates an overall circuit model 700 for the Travelling Wavetransceiver of FIG. 5.

As an example, the circuit of FIG. 5 has been simulated assuming a 1×4LED array transmitting to a 1×4 detector array and using equivalentcircuit models representing each micro-LED and micro-detector. Theoptical paths were simulated as delays due to the short distancesinvolved. In this approach, in effect, the capacitances and parasiticresistances of the micro-LEDs and detectors are absorbed by thetravelling wave circuits. FIG. 8 illustrates the simulated S-parametersof the two-port system. Preliminary simulations indicate that over 20GHz broadband operation of the LED/detector transceiver. With additionalmicro-LED and micro-Detectors in FIG. 5, the operating bandwidth can beextended to 40 GHz and beyond. The graph 800 of FIG. 8 depicts anelectrical simulation of the disclosed optical wireless link.

The electrical gain (S₂₁) in FIG. 8 is from the TIA which compensatesfor path losses. This gain was lumped with the gain of thephoto-detector for this simulation. The important characteristics fromthis simulation are the gain flatness and minimum port reflections (S₂₂,S₂₂) over 20 GHz bandwidth. This approach may dramatically increase theoperation bandwidth of LED/DETECTOR transceiver for wireless opticalcommunications.

Ultra-High Speed LEDs for Wideband Wireless Optical Communication

This section describes material structures and device designs forultra-high-speed LEDs suitable for wideband wireless opticalcommunication. The material structures are designed to improve theintrinsic spontaneous emission and recombination rates such that the LEDoptical signal can respond and follow to ultra-high frequency electricalstimulations. Different single and multi-quantum well materialstructures based on GaAs, GaSb and GaN substrates are devised foroperating wavelengths from infra-red to ultra-violet range.Multi-wavelength wireless optical transceivers based on these materialscan be constructed as described earlier to achieve higher data rates andpoint-to-multipoint networking communication. Disclosed herein are bothlattice-matched and strained-layer, super-lattice (SSL) structures.Quaternary SSL material structures based on GaAs and GaN substrates havesuccessfully been developed for cascaded multi-junction solar cells,LEDs and photo-detectors operating in static DC conditions. Disclosedherein are material structures that enable ultra-high-speed operation ofLEDs and detectors.

Ultra-High Speed LED with Carrier Confinement Layer

An ultra-high speed LED epitaxial structure 900 is shown in FIG. 9. TheLED structure 900 includes an n+ doped (high n doped) GaAs contactlayer, n doped GaAs layer, n doped carrier confinement layer (CCL),undoped n-side barrier, undoped quantum well (QW), undoped p-sidebarrier, p doped GaAs layer and p+ doped GaAs contact layer. The lowband gap InGaAs QW sandwiched between two wide band gap GaAsP barriersis the active region of the device. The electrons are supplied from then-doped layers and the holes are supplied from the p-doped layers to theQW. Due to the carrier confinement in the QW, radiative recombinationoccurs resulting in the emission of light. The recombination dynamics isone of the factors that limits the switching time of an LED. The carrierlifetime can be considerably reduced by having a high concentration ofinjected carriers in the active region. In a QW in which free carriersconfine in a small active region is employed to obtain high carrierconcentration and thus short carrier lifetimes. The spontaneous lifetimeof a semiconductor is given by equation 1.

$\begin{matrix}{\tau_{spont} = \frac{1}{BN_{D,A}}} & {{equation}\mspace{14mu} 1}\end{matrix}$

Within equation 1, B is the bimolecular recombination coefficient andN_(D,A) is the impurity concentration. The bimolecular recombinationcoefficient is related to the equilibrium recombination rate R₀ byequation 2.

$\begin{matrix}{B = \frac{R_{0}}{n_{i}^{2}}} & {{equation}\mspace{14mu} 2}\end{matrix}$

Within equation 2, n_(i) is the intrinsic carrier concentration. Forbulk GaAs, R₀=7.9×10² cm⁻³s⁻¹ and B=2.0×10⁻¹° cm³s⁻¹. The value ofspontaneous lifetime τ_(spont) is 5.1×10⁻⁹ s for a majority carrierconcentration of 10¹⁸ cm³. In a bulk semiconductor, the recombinationoccurs over a large region since the minority carriers are distributedover a large distance and the majority carrier concentration decreasesas these carriers diffuse into the adjacent region. The largerecombination region in bulk material increases the recombinationlifetime of the carriers. The radiative recombination rate is not anintrinsic property of the material; with the increasing carrierconcentration in the active region, the radiative recombination rateincreases and the spontaneous lifetime decreases. In a quantum wellstructure, the carriers are confined to the active region by means ofthe barriers. As a result, the thickness of the region in which thecarriers recombine is given by the thickness of the active region ratherthan the diffusion length. Due to the high carrier concentration in aquantum well structure, the radiative recombination time is reduced andthe LED can be operated in the high frequency (˜20 GHz) zone.

The percentage of Indium composition (In %) is significant indetermining the peak emission wavelength. For achieving high efficiencyof the LED device, the light emitted from the active region should betransparent to the substrate material. For 23% Indium, the peak emissionwavelength is 998 nm which is transparent to the GaAs substrate. Theatmospheric optical window in the infrared region of the spectrum isbetween 850 nm to 1200 nm. It is highly important for wireless opticalcommunication that the peak emission wavelength of the emitter is withinthe atmospheric window. The indium percentage in the QW is selected toalso meet the above criteria. The Indium composition is altered higherto 30% or lower than 20% depending on the requirement of the wavelengthof the emitted light. The percentage of Phosphorus (P) composition isselected to obtain optimum barrier height for the QW region with theobjective to achieve high carrier confinement in the QW and highoperating speed. Carriers tend to escape from the active layer of an LEDinto the confinement layers. The electron/hole escape rate can besubstantial in double heterostructures depending on theconduction/valence band offsets. For the In_(0.23)GaAs/GaAsP_(0.45)material system, the conduction band offset is as high as 0.65 eV but ithas a lower valance band offset of 0.23 eV. Therefore, the leakage ofholes in the n-side of the barrier is significant. By incorporating awide band gap layer at the n-side barrier the hole leakage is reducedwhich improves the carrier confinement in the active region. The wideband-gap carrier confinement layer (CCL) plays an important role indetermining the efficiency, luminous power output and the speed of theLED. The n-doped CCL must supply electrons to the QW and at the sametime act as a barrier layer to block the leakage of holes from the QW. Athick (>100 Å) GaAsP with 60% P can act as CCL. But GaAsP is latticemismatched to GaAs, the maximum thickness of GaAsP layer with 60% Pwhich can be grown before it relaxes is 82.5 Å. Therefore, a thick (>100Å) GaAsP with 60% P CCL will result in deteriorating the reliability ofthe device. To alleviate this issue, alternate thin layers of wide bandgap materials GaAsP and InGaP are used as CCL. FIG. 10 illustrates anLED epitaxial structure 1000 with three alternate layers of GaAsP (60%P) and InGaP (48.5% In) act as CCL (STR#1). The thickness of each layeris 35 Å. Therefore the thickness of GaAsP (60% P) is below its criticalthickness of strain relaxation and InGaP with 48.5% Indium is latticematched to GaAs. FIG. 11 illustrates another LED epitaxial structure1100 with two alternate layers of GaAsP (60% P) and InGaP (48.5% In)acting as CCL (STR#2). FIG. 12 depicts a simpler epitaxial structure1200, having a single layer of GaAsP (60% P) and InGaP as CCL (STR#3).The design parameters of the LED structures are summarized in TABLE 2,TABLE 3, and TABLE 4. TABLE 5 lists the design parameters of the LEDwith 23% In composition in the QW and 45% P in the barriers.

A comparison of the efficiency and luminous power output of the LED ofstructure designs STR#1, STR#2, STR#3 and with CCL=100 Å GaAsP (P=60%)(STR#4), and CCL=1000 Å InGaP (In=48.5%) (STR#5) is shown in graph 1300of FIG. 13. LED STR#1 gives high efficiency (>60%) at high (>2.0V)forward bias voltage. TABLE 6 shows the luminous power and efficiencyfor different anode voltages of STR#1, 2 & 3. FIG. 14 illustrates agraph 1400 of a 10 GHz transient response at 1.7 V of LED STR#3. FIG. 15illustrates a graph 1500 of a 20 GHz transient response at 1.7 V of LEDSTR#3. The graphs 1600 and 1700 of FIG. 16 and FIG. 17, respectivelyshow the DC characteristics and 10 GHz transient response at 1.7 V ofthe single QW InGaAs/GaAsP LED with 23% In composition in the QW and 45%P in the barriers.

The composition of phosphorous can be reduced to 40% or further to 35%to improve the device transient response while maintaining straincompensation by altering the thickness of the QW and barrier layers. Aspectral diagram 1800 of LED STR#3 is shown in FIG. 18, the peakemission wavelength is 998 nm. The electron leakage from the QW regionto the p-layer can be reduced by incorporating a wide band gap AlGaAs orGaAsP electron blocking layer (EBL) above the p-side barrier. Since theInGaP with 48.5% Indium (latticed matched to GaAs) has a larger valanceband offset when interfaced with InGaAs, it can be used as a holeblocking layer (HBL) which improves the efficiency of the LED at highervoltages drastically. The InGaP layer interfaces with the InGaAs QW andreplaces the n-GaAsP barrier. GaAsP layer is used as the p-side barrier.Two and multiple quantum wells (MQW) InGaAs/GaAs LED designs can also beused as ultra-high speed emitters in wireless visual lightcommunication.

Design parameters of LED structure #1 are shown in TABLE 2.

TABLE 2 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 45% P 35 — — QW InGaAs23% In 70 — — Barrier GaAsP 60% P 30 — — n layer GaAsP 60% P 35 n.type 3× 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n layer GaAsP 60% P 35n.type 3 × 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n layer GaAsP60% P 35 n.type 3 × 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n+contact GaAs — 10000 n.type 3 × 10¹⁹ layer

Example of design parameters of LED structure #2 are shown in TABLE 3.

TABLE 3 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 45% P 35 — — QW InGaAs23% In 70 — — Barrier GaAsP 60% P 30 — — n layer GaAsP 60% P 35 n.type 3× 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n layer GaAsP 60% P 35n.type 3 × 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n+ contactGaAs — 10000 n.type 3 × 10¹⁹ layer

Design parameters of LED structure #3 are shown in TABLE 4.

TABLE 4 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 45% P 35 — — QW InGaAs23% In 70 — — Barrier GaAsP 60% P 30 — — n layer GaAsP 60% P 30 n.type 3× 10¹⁹ n layer InGaP 48.5% In 1000 n.type 3 × 10¹⁹ n+ contact GaAs —10000 n.type 3 × 10¹⁹ layer

Design parameters of LED with 23% In composition in the QW and 45% P inthe barriers are shown in TABLE 5.

TABLE 5 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 45% P 35 — — QW InGaAs23% In 70 — — Barrier GaAsP 45% P 30 — — n layer GaAsP 45% P 30 n.type 5× 10¹⁸ n layer InGaP 48.5% In 500 n.type 5 × 10¹⁸ n+ contact GaAs —10000 n.type 5 × 10¹⁸ layer

A comparison of efficiency and luminous power output of the three LEDstructures is shown in TABLE 6.

TABLE 6 LED STR# 1 LED STR# 2 LED STR# 3 Voltage Luminous LuminousLuminous levels Effi- Power Effi- Power Effi- Power (V) ciency (mW)ciency (mW) ciency (mW) 1.6 79.8% 8.2 79.8% 8.3 79.8% 8.3 1.7 76.9% 23.376.9% 23.6 76.9% 23.9 1.8 74.7 46.6 74.8% 47.6 74.5% 48.3 2.0  63% 103.057.8% 105.5  23% 103.0

A comparison of DC efficiency and luminous output power of 1×1000μ2single QW InGaAs/GaAsP LED with 23% in composition in the QW and 45% Pin the barriers is shown in TABLE 7.

TABLE 7 Voltage levels (V) Efficiency Luminous Power (mW) 1.6 81.5% 26.21.7  79% 50.9 1.8 72.8% 79.3 1.9  50% 108.8

Light is extracted from the top surface of the LED. To increase theefficiency of the light extraction, the p+ electrode(s) are required tooccupy minimum area on the top surface of the device. Under transientcondition the performance of the LED highly depends on the currentspreading from the p+ electrodes since the radiative recombination ratedepends on the current spreading in the p+/p layers to the QW region.For efficient transient performance the current should spread across theentire active region. The number of p+ electrodes, the spacing betweenthem, the thickness and the doping concentration of the p+ and the players play crucial role in determining the current spreading to theactive region of the device. Increasing the number of p+ electrodes anddecreasing the spacing between them will improve the transientperformance of the LED but it will reduce the top surface open area andthus will degrade the light extraction efficiency. The trade-off betweenthe extraction efficiency and the transient performance is investigatedand the device performance of various p+ electrode designs is analyzed.A diagram 1900 of FIG. 19 illustrates the current (y-component)spreading of a 5μ LED with three p+ electrodes each of 0.7μ on top. Thestructure has a top open area of 58% and the spacing between theadjacent electrodes is 1.45μ. A diagram 2000 shown in FIG. 20 depictsthe current spreading in the p+ layer is increased by embedding the p+electrodes in the p+ layer. The current spreading is improved when theelectrodes are embedded in the p+ layer because the current from theelectrodes is injected across two dimensions—the bottom and the sides ofthe p+ electrodes. The length of the p+ electrodes and the open areapercentage are 0.7μ and 58% respectively. The transient performance canbe improved by reducing the spacing between the p+ electrodes and thelight extraction efficient can be increased by increasing the percentageof open area. The new device design with more number of p+ electrodes ofsmaller dimension meets the above criteria. A diagram 2100, shown inFIG. 21, depicts the LED structure with five p+ electrodes each of 0.3μlength. The space between two adjacent electrodes is 0.95μ and thepercentage of open area is 70%. A graph 2200 shown in FIG. 22 depicts acomparison of the 10 GHz transient response of the devices withdifferent p+ electrode designs. TABLE 8 describes the design parametersof the different device designs. Light can also be extracted from theback-side of the device using flip-chip design.

TABLE 8 Spacing P+ between two P+ Device Number electrode adjacent p+layer Percentage Length of p+ length electrodes thickness of open (μ)electrodes (μ) (μ) (μ) area 5 3 1.0 1.00 0.1 40% 5 3 0.7 1.45 0.1 58% 53 0.7 1.45 0.2 58% 5 3 0.7 1.45 0.2 58% (embedded) 5 5 0.3 0.95 0.1 70%5 (flip- 1 5.0 — 0.1 Light is chip) extracted from back-side 4 2 0.71.30 0.1 65% 3 2 0.7 0.80 0.1 53% 3 2 0.5 1.00 0.1 67% 2 1 0.7 — 0.1 65%

A diagram 2300 shown in FIG. 23. is a top view of the LED and depictsthe current spreading across the z-dimension. This current spreading iscritical in evaluating the transient performance of the LED. The anodecontacts are connected to the metal strips (p+ electrodes). The lengthand width of the metal strips determine the current spreading across thez-dimension. The metal strip consists of a stack of 100 Å thickTitanium, 100 Å Platinum (or Palladium) and 6800 Å Gold as shown indiagram 2400 of FIG. 24. A comparison of the transient response ofdevices of width 100μ, 150μ, 200μ and the ideal structure is shown ingraph 2500 of FIG. 25. The transient performance deteriorates when theLED width is increased beyond 100μ. TABLE 9 summarizes the designparameters of LED of different widths. The LED structure with two n+electrodes each of 5μ with 1μ spacing from the active mesa is shown indiagram 2600 of FIG. 26. The 20 GHz optical response to sinusoidalvoltage waveform of the LED structure is shown in graph 2700 of FIG. 27.

TABLE 9 Transient Device widths (μ) Metals Metal thicknesses (Å)Performance 25 Ti/Pt/Au 100/100/6800 Excellent 50 Ti/Pt/Au 100/100/6800Excellent 100 Ti/Pt/Au 100/100/6800 Excellent 150 Ti/Pt/Au 100/100/6800GoodUltra-High Speed AlGaAs/GaAs LED

AlGaAs/GaAs LED can be designed for ultra-high speed applications. FIG.28 illustrates epitaxial stack diagram 2800 of an ultra-high speedsingle GaAs QW with AlGaAs barriers LED structure. TABLE 10 summarizesthe design parameters of the AlGaAs/GaAs LED. The electron leakage fromthe QW into the confinement layers in the AlGaAs/GaAs structure ishigher than the hole leakage due to the usually larger diffusionconstant of electrons compared with holes in III-IV semiconductors. Thecarrier confinement in the GaAs QW can be improved by incorporating ap-doped wide band gap (AlGaAs) electron blocking layer (EBL) at thep-side barrier. The design parameters of the single QW AlGaAs/GaAs LEDwith EBL are illustrated in TABLE 11. Although the growth process ofAlGaAs/GaAs material systems is simple, the disadvantage of using GaAsQW is that the light emitted from the active region is absorbed in theGaAs substrate which reduces the output optical efficiency of theAlGaAs/GaAs LED. FIG. 29 illustrates a graph 2900 of the luminous powerand the (internal) efficiency of the single QW AlGaAs/GaAs LED. At 1.7 Vthe output luminous power is 60 mW and the efficiency is 76.4%. A 10 GHztransient response at 1.7 V of the single QW AlGaAs/GaAs LED is shown ingraph 3000 of FIG. 30. The peak emission wavelength of the AlGaAs/GaAsLED is 810 nm which is shown in graph 3100 of FIG. 31.

Design parameters of single QW AlGaAs/GaAs LED are shown in TABLE 10.

TABLE 10 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier AlGaAs 45% Al 30 — — QW GaAs— 70 — — Barrier AlGaAs 35% Al 30 — — n layer AlGaAs 25% Al 30 n.type 5× 10¹⁸ n layer AlGaAs 25% Al 1000 n.type 5 × 10¹⁸ n+ contact GaAs —10000 n.type 5 × 10¹⁸ layer

Design parameters of single QW AlGaAs/GaAs LED with EBL are shown inTABLE 10.

TABLE 11 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer AlGaAs 45% Al 1000 p.type 2 × 10¹⁹ Barrier AlGaAs 45% Al 30 — —QW GaAs — 70 — — Barrier AlGaAs 35% Al 30 — — n layer AlGaAs 25% Al 30n.type 5 × 10¹⁸ n layer AlGaAs 25% Al 1000 n.type 5 × 10¹⁸ n+ contactGaAs — 10000 n.type 5 × 10¹⁸ layerUltra-High Speed InGaN/GaN LED

InGaN is the primary material for high brightness blue and green LEDs.Due to the large band offset in the InGaN/GaN material system a highradiative efficiency is observed despite the presence of a highconcentration of threading dislocations in InGaN/GaN epitaxial films.These threading dislocations are due to the lattice mismatch between thecommonly used sapphire and SiC substrates and the GaN and InGaNepitaxial films. Typical densities of the threading dislocations are inthe range of 10⁷-10⁹ cm⁻². InGaN/GaN QW LEDs cover the wide range fromthe visible light to deep ultraviolet. For 11% Indium composition inInGaN QW, the peak emission wavelength is 450 nm which is in the visiblerange of the spectrum. The percentage of the Indium composition in theInGaN QW is significant in determining the speed of the InGaN/GaN LED.Less Indium composition (<10%) results in poor carrier confinement inthe well region which decreases the radiative recombination rate andhigher Indium composition (>15%) results in poor transient response dueto increased band offset between the QW and barrier. Due to the inherentlow mobilities of GaN material systems (400 cm²V⁻¹s⁻¹ for electrons and100 cm²V⁻¹s⁻¹ for holes) the thickness of the layers is reduced forimproving the transient response of the InGaN/GaN LED. An epitaxialstructure 3200 of InGaN/GaN LED designed for ultra-high speed operationis shown in FIG. 32. The percentage of Indium composition in the InGaNQW is 11% with AlGaN (20% Al) barriers. The luminous output power andefficiency versus the anode voltage of the single QW InGaN/GaN LED isshown in graph 3300 of FIG. 33. The luminous output power and efficiencyof the device at 3.5 V are 304 mW and 90% respectively. TABLE 12 liststhe values of luminous output power and efficiency of the single QWInGaN/GaN LED for different voltage levels. The luminous output powerand efficiency of the InGaN/GaN devices are higher than that of the GaAsbased LEDs. A graph 3400 of the 10 GHz transient response at 3.5 V and agraph 3500 of the emission spectrum of the InGaN/GaN LED with 11% Indiumin the InGaN QW are shown in FIG. 34 and FIG. 35 respectively. The peakemission wavelength for 11% Indium in the InGaN QW is 400 nm. The peakemission wavelength can be stretched to the blue region of the spectrumby increasing the Indium composition in the InGaN QW. But increasing theIndium composition in the InGaN QW results in larger band offsets thusdeteriorating the transient performance of the LED. For higher Indiumpercentage (20% In) in the QW, the speed of the LED can be improved byreplacing the wide band-gap p-side AlGaN barrier with GaN. The peakemission wavelength for this structure is 435 nm. TABLE 13 and 11summarize the design parameters of the ultra-high speed InGaN/GaN LEDs.Wide band gap InAlN layer with 17% Indium can be incorporated at boththe “p” and “n” side barriers as EBL/CCL to improve the carrierconfinement in the QW region. At 17% Indium composition InAlN is latticematched to GaN. The transient performance of the InGaN/GaN LED with 11%Indium composition in the InGaN QW is improved by reducing the distancebetween the n+ electrode and the mesa from 1μ to 0.5μ as shown inepitaxial diagram 3600 of FIG. 36. The 20 GHz optical response tosinusoidal voltage waveform of the LED structure is shown in graph 3700of FIG. 37. It is difficult to obtain high p+ doping in GaN. Due thisconstraint, the p+ electrode is spread across the entire p+ contactlayer for better current spreading and light is extracted from thebackside of the device using flip-chip technology as shown in diagram3800 of FIG. 38.

A comparison of luminous power and efficiency of InGaN/AlGaN LED with11% Indium in the InGaN QW is shown in TABLE 12.

TABLE 12 Voltage level (V) Luminous Power (mW) Efficiency 3.3 51.594.7%  3.5 304 90.5%  3.7 635 74% 3.8 760 52% 4.0 915 25%

Design parameters of InGaN/AlGaN LED with 11% Indium composition in theInGaN QW are shown in TABLE 13.

TABLE 13 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaN — 100 p.type 5 × 10¹⁸ layer player GaN — 100 p.type 1 × 10¹⁸ Barrier AlGaN 20% Al 35 — — QW InGaN 11%In 70 — — Barrier AlGaN 20% Al 30 — — n layer AlGaN 30% Al 30 n.type 2 ×10¹⁹ n+ contact GaN — 10000 n.type 2 × 10¹⁹ layer

Design parameters of InGaN/AlGaN LED with 20% Indium composition in theInGaN QW are shown in TABLE 14.

TABLE 14 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaN — 100 p.type 5 × 10¹⁸ layer player GaN — 100 p.type 1 × 10¹⁸ Barrier GaN — 35 — — QW InGaN 20% In 70— — Barrier GaN — 30 — — n layer AlGaN 20% Al 30 n.type 2 × 10¹⁹ n+contact GaN — 10000 n.type 2 × 10¹⁹ layerUltra-High Speed InGaSb/AlGaSb LED

Most of the infrared light is absorbed by water vapor and carbon dioxideof earth's atmosphere. The earth's atmosphere causes another problem inthe infrared transmission, the atmosphere itself radiates strongly inthe infrared, often putting out more infrared light that the emitter. Inthe infrared window of 0.8μ-1.2μ wavelength, the atmospheric absorptionis less and emission is low and in the range of 1.5μ-2.4μ wavelength theatmospheric absorption is less and emission is very low. Therefore, forlong distance wireless backhaul, using carrier wavelength in the rangeof 1.5μ-2.4μ will be more advantageous. The peak emission wavelength ofInGaSb/AlGaSb LEDs is in the range of 1.4μ-2.0μ. By selecting the properIndium composition in the InGaSb QW, the peak emission wavelength isoptimized. The carriers are confined in the narrow band gap (˜0.65 eV)InGaSb QW by sandwiching it between wide band gap (˜1.3 eV) AlGaSbbarriers. The LED device is grown on GaSb substrate. An epitaxialstructure 3900 of the ultra-high speed InGaSb/AlGaSb LED is shown inFIG. 39. TABLE 15 lists the design parameters of the InGaSb/AlGaSb LED.

The luminous output power and efficiency versus the applied voltage ofthe single QW InGaSb/AlGaSb LED is shown in graph 4000 of FIG. 40. Theluminous output power and efficiency of the device at 0.8 V are 1.8 mWand 93.6% respectively. TABLE 16 lists the values of luminous outputpower and efficiency of the single QW InGaSb/AlGaSb LED for differentvoltage levels. The 10 GHz transient response at 0.8 V of InGaSb/AlGaSbLED is shown in graph 4100 of FIG. 41. The InGaSb/GaSb emission spectrumis shown in graph 4200 of FIG. 42. The peak emission wavelength is1.68μ. This wavelength falls in the sweet spot of the infraredatmospheric window where the atmospheric absorption and emission areminimal. Design parameters of ultra-high speed InGaSb/AlGaSb LED areshown in TABLE 15.

TABLE 15 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaSb — 500 p.type 4 × 10¹⁹ layerp layer AlGaSb 35% Al 500 p.type 3 × 10¹⁹ Barrier AlGaSb 35% Al 35 — —QW InGaSb 25% In 70 — — Barrier AlGaSb 45% Al 35 — — n layer AlGaSb 45%Al 600 n.type 3 × 10¹⁹ n+ contact GaSb — 5000 n.type 3 × 10¹⁹ layer

A comparison of luminous power and efficiency of InGaSb/AlGaSb LED with25% Indium composition in the InGaSb QW is shown in TABLE 16.

TABLE 16 Voltage level (V) Luminous Power (mW) Efficiency 0.8 1.80 93.6%0.9 6.06 86.9% 1.0 13.1 66.0%Ultra-High Speed PhotodetectorUltra-High Speed MQW Photodetector

Photodetectors convert optical signals into electrical signals. Whenlight is incident on a semiconductor excess electrons and holes aregenerated which increases the conductivity of the material. This changein the conductivity upon light incidence is the basis of thephotodetector. A photodetector is a p-i-n junction diode operated in thereverse bias mode. If the electrons and holes are generated within thespace charge depletion region of the p-i-n diode, then they will beseparated by the electric field and a current will be produced. But ifthe carriers are generated in the diffusion region, they will berecombined with the majority carriers in the region resulting in poorefficiency of the photodetector. The photo-generation in the diffusionregion will also degrade the transient performance of the device due tothe slow time-constant related to the minority carrier recombination. Inthe case of MQW structure, it is very important that the QW regions arecompletely depleted. The QW layers are undoped and act as i-layer, so atzero bias all the QW layers are depleted. But when light is shone on thedevice due to the generation of carriers the QWs close to the side oflight incidence become undepleted. The applied reverse bias voltageshould be such that the entire active region of the device is depleted.

Ultra-high speed photodetectors are designed using multiple quantumwells (MQW) GaAs based structures. The concentration of thephoto-generated carriers can be increased by increasing the number ofquantum wells. The typical operating voltage for most ultra-high speedapplications is ˜2.7 V (USB 3.0 specification). FIG. 43 illustrates aconduction band diagram 4300 of a ten QW layer structure at 2.7 and 5volts reverse bias. For the given structure at 2.7 V, 450 Å of i-layeris depleted. 4 QWs each of 70 Å and 5 barriers each of 35 Å can beincluded in a region of 450 Å. Photodetector structures with more than 4QWs must be operated at higher than 2.7V reverse bias to obtain higherspeed and efficiency of the device. FIG. 44 illustrates a diagram of afour QW layer InGaAs/GaAs photodetector epitaxial structure 4400. Thephotodetector design parameters are summarized in TABLE 17. For 23%Indium composition in the InGaAs QW, the photodetector cutoff wavelengthis 1.12μ as shown in graph 4500 of FIG. 45. The light of wavelength 998nm emitted from the LED with 23% Indium composition in the QW will beabsorbed to generate electrons and holes.

An example of the four QW InGaAs/GaAs ultra-high speed photodetectordesign is shown in TABLE 17.

TABLE 17 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 45% P 35 — — QW InGaAs23% In 70 — — Barrier GaAsP 45% P 35 — — QW InGaAs 23% In 70 — — BarrierInGaP 45% P 35 — — QW InGaAs 23% In 70 — — Barrier InGaP 45% P 35 — — QWInGaAs 23% In 70 — — Barrier GaAsP 60% P 30 — — n layer GaAsP 60% P 30n.type 5 × 10¹⁸ n layer InGaP 48.5% In 1000 n.type 5 × 10¹⁸ n+ contactGaAs — 10000 n.type 5 × 10¹⁸ layer

For the 4 QWs InGaAs/GaAsP photodetector, the photo-generated current isin the range of 2×10⁻⁴ Acm⁻². The photo-generated current is increasedto higher levels by increasing the device area and also by usingmultiple fingers. A single QW and 10 QWs InGaAs/GaAsP photodetector arealso designed. The single QW photodetector will give excellent transientperformance. The 10 QW photodetector is operated at higher reverse biasvoltage (>5 V) to deplete the entire active region of the device. TABLE18 shows the photo-generated current under 10 GHz transient response for1, 4, 10 and 20 QW structures.

TABLE 18 Photo-generated current Operating Voltage Number of QWs (Acm⁻²)(V) 1 5 × 10⁻⁵ 2.7 (or lesser) 4 2 × 10⁻⁴ 2.7 10 5 × 10⁻⁴ 5 20 1 × 10⁻³10

Due to the low photo-generated current density in the device, thecurrent spreading in the p+ layer which depends on the number of p+electrodes and the spacing between them does not degrade the transientperformance of the photodetector unlike the LED. A photodetector oflength 10μ is shown in epitaxial structure 4600 of FIG. 46. Aphotodetector of length 20μ is shown in epitaxial structure 4700 of FIG.47 and a photodetector of length 50μ is shown in epitaxial 4800 of FIG.48. For the 10μ and 20μ devices, two p+ electrodes each of 1μ length areconnected on the top surface of the device and for the 50μ device fourp+ electrodes each of 1μ are connected to the p+ layer. In one design 3p+ electrodes are incorporated for (L=) 20μ device. Two n+ electrodeseach of 5μ length are connected to the n+ layer with 1μ spacing from themesa. TABLE 19 shows the electrode design parameters of different devicelengths of InGaAs/GaAsP photodetector. A comparison of the generatedphoto-current at 10 GHz transient responses at 2.7 V for single QWInGaAs/GaAsP photodetector of lengths 10μ, 20μ and 50μ is shown in graph4900 of FIG. 49.

TABLE 19 Device Length of p+ Length of n+ length Number of p+ electrodesNumber of n+ electrodes (μ) electrodes (μ) electrodes (μ) 10 2 1 2 5 202 1 2 5 50 4 1 2 5Ultra-High Speed GaN Based Photodetector

MQW GaN based photodetector can be used in ultra-high speedtelecommunication. An epitaxial structure 5000 of the ultra-high speedInGaN/AlGaN photodetector design is shown in FIG. 50. The number of QWscan be increased to increase the photo-generated current. The percentageIndium composition is increased to 30% and the AlGaN barriers arereplaced to GaN to detect the signal emitted from the InGaN/GaN LED with20% Indium composition in the QW.

Ultra-High Speed InGaSb/GaSb Photodetector

MQW InGaSb/GaSb photodetector can detect infrared signals in thewavelength range of 1.4μ to 2.0μ. An epitaxial structure 5100 of theultra-high bandwidth InGaSb/GaSb photodetector is shown in FIG. 51. Thenumber of QWs can be increased to increase the photo-generated current.

Ultra-High Speed Integrated LED and Photodetector

The LED and the photodetector have similar structures. MQW devicestructures can be used as LED in the forward bias mode and as aphotodetector in the revise bias mode. The LED can be integrated into asingle three terminal device 5200 as shown in FIG. 52. The photodetectorcan be integrated into single three terminal device 5300 as shown inFIG. 53. The single QW LED sits on top of the MQW detector. Since thesignal to be detected is emitted from the smaller band gap materials(InGaAs/InGaN) compared to the substrate materials (GaAs/GaN), it istransparent to the ‘n’ and ‘p’ layers of the LED and very minimumabsorption takes place in the single QW of the LED. The light to bedetected is shone on the top surface of the device and the absorptiontakes place in the QWs of the detector which generates (photo) currentin the device.

Novel Ultra-High Speed Wireless Communication Using LED WavelengthModulation Technique

To achieve higher sensitivity of detection than by using amplitudemodulation, wavelength modulation technique is applied usingInGaAs/GaAsP, InGaSb/AlGaSb and InGaN/AlGaN LEDs and photodetectors. Thewavelength of single QW LED can be modulated by biasing the device atdifferent voltages. At low bias the carriers fill up the low energylevels and the peak emission wavelength corresponds to the band gapenergy. With increasing bias the injection of the carriers increases inthe QW and the carriers occupy the higher energy levels. The peakemission spectra at higher biases shifts to lower wavelengths.Therefore, by changing bias the wavelength of the emitted light can bealtered.

In the wavelength modulation scheme using single LED, the device must bealways “ON”. FIG. 54 illustrates a graph 5400 of the emission spectra at1.6 V and 1.9 V of single QW InGaAs/GaAs LED. The percentage compositionof Indium (In) in the QW of the LED is 23% and the percentagecomposition of phosphorous (P) in the p-side and n-side barriers are 45%and 60% respectively. As shown in FIG. 54, a 97 nm shift in thewavelength is observed for the InGaAs/GaAs LED when the applied bias ischanged from 1.6 V to 1.9 V. The output luminous power and efficiency ofthe LED is shown in graph 5500 of FIG. 55. The design parameters of theLED are given in TABLE 20. The separation between the peak emissionspectra wavelengths at two different biases can be increased byincreasing the depth of the QW. By increasing the percentage compositionof Indium in the QW and the percentage composition of phosphorous in thebarriers, the depth of the QW is increased. The design parameters ofsingle QW LED with 30% In in the well and 60% P in the barriers aregiven in TABLE 21. The emission spectra at 1.6 V and 1.9 V of single QWInGaAs/GaAsP LED with 30% In and 60% P is shown in graph 5600 of FIG.56. A 144 nm shift in the wavelength is observed when the applied biasis changed from 1.6 V to 1.9 V. The design parameters of single QW LEDwith 30% Indium in the well and 45% P in the barriers is given in TABLE22. The emission spectra at 1.6 V and 1.9 V of the LED is shown in graph5700 of FIG. 57. A 153 nm shift in the wavelength is observed when theapplied bias is changed from 1.6 V to 1.8 V. The output luminous powerand efficiency of the LED is shown in graph 5800 of FIG. 58. The 10 GHztransient response of the LED at 1.6 V and 1.8 V is shown in graph 5900of FIG. 59.

Design parameters of single QW InGaAs/GaAs LED with 23% In, 45% P inp-side barrier and 60% P in n-side barrier are shown in TABLE 20,

TABLE 20 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 45% P 35 — — QW InGaAs23% In 70 — — Barrier GaAsP 60% P 30 — — n layer GaAsP 60% P 35 n.type 3× 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n layer GaAsP 60% P 35n.type 3 × 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n layer GaAsP60% P 35 n.type 3 × 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n+contact GaAs — 10000 n.type 3 × 10¹⁹ layer

Design parameters of single QW InGaAs/GaAs LED with 30% In in the well,60% P in p-side barrier and n-side barrier are shown in TABLE 21.

TABLE 21 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 60% P 35 — — QW InGaAs30% In 70 — — Barrier GaAsP 60% P 30 — — n layer GaAsP 60% P 35 n.type 3× 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n layer GaAsP 60% P 35n.type 3 × 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n layer GaAsP60% P 35 n.type 3 × 10¹⁹ n layer InGaP 48.5% In 35 n.type 3 × 10¹⁹ n+contact GaAs — 10000 n.type 3 × 10¹⁹ layer

Design parameters of single QW InGaAs/GaAs LED with 30% In in the well,45% P in the barriers are shown in TABLE 22.

TABLE 22 Doping Percentage Thickness Doping Concentration Layer MaterialComposition (Å) Type (cm⁻³) p+ contact GaAs — 1000 p.type 4 × 10¹⁹ layerp layer GaAs — 1000 p.type 2 × 10¹⁹ Barrier GaAsP 45% P 35 — — QW InGaAs30% In 70 — — Barrier GaAsP 45% P 30 — — n layer GaAsP 45% P 30 n.type 5× 10¹⁸ n layer InGaP 48.5% In 1000 n.type 5 × 10¹⁸ n+ contact GaAs —10000 n.type 5 × 10¹⁸ layerWavelength Division Multiplexing Using Ultra-High Speed LEDs andPhotodetectors

By using two LEDs operating at two different wavelengths, multiplewavelength communication or wavelength division multiplexing (WDM)technique is achieved. In this technique, the LEDs are switched ON andOFF as in on-off keying scheme. As shown in block diagram 6000 of FIG.60, LED 1 and LED2 emit light at different wavelengths ‘λ₁’ & ‘λ₂’respectively. The detector 1 is designed to pick the signal from LED 1of wavelength λ₁ and the detector 2 is designed to detect the emittedlight of LED2 of wavelength λ₂.

Single QW InGaAs/GaAsP LED1 and LED2 have different percentage of Indiumin the QW and they emit light of different wavelengths. The InGaAs/GaAsPdetectors are designed so that for the detector 1 the cutoff wavelengthis greater than (or equal to) λ₁ and for the detector 2 the cutoffwavelength is greater than (or equal to) λ₂. Different material systemcan also be implemented for the LEDs and detectors. For example,InGaAs/GaAsP material system can be implemented for LED1 and detector 1which will emit light and absorb in the infrared region of the spectrumrespectively and InGaN/AlGaN material system can be used for LED2 anddetector 2 which will emit and absorb light in the violet/blue regionrespectively. Due to the large separation of emitted wavelengths fromthe two LEDs, the detection of the signals will be more efficient.

Full Duplex Ultra-High Speed Telecommunication Using LEDs andPhotodetectors

A full-duplex communication system where two connected devices that cancommunicate simultaneously can be designed by using two LEDs and twodetectors emitting and absorbing light at different wavelengths. Thebi-directional communication set-up using two LEDs and two detectors isshown in block diagram 6100 of FIG. 61.

The wavelength modulation technique can be also implemented using twoLEDs emitting light at different wavelengths integrated into onethree-terminal device. The n+/n layers are at the top and bottom in thestructure and are connected to the n+ electrodes and the p+/p layers arecommon to both the LEDs in one design as shown in epitaxial stack 6200FIG. 62. In another design, the p+/p-layers are at the top and bottom inthe structure and are connected to the n+ electrodes and the n+/n layersare common to both the LEDs as shown in epitaxial stack 6300 of FIG. 63.QW1 emits light of wavelength ‘λ₁’ and QW2 emits light of wavelength‘λ₂’. The p-layer is common to both the LEDs which is connected to thep+ electrode (third terminal).

Ultra-High Speed Photodetector Design to Detect Signals of DifferentWavelengths

The photodetector design to detect signal of two different wavelengthsis shown in schematic 6400 of FIG. 64. The cutoff wavelength of detector1 is λ₁ and that of detector 2 is λ₂ (<λ₁) as shown in graph 6500 ofFIG. 65. In the wavelength modulation scheme using single LED, at lowbiases the peak emission wavelength of the emitted signal is λ₁ and athigher biases the peak emission wavelength λ₂ (shorter than 2) whichwill also encompass wavelength λ₂. At lower bias detector D1 will pickup the signal of wavelength λ₁ and at higher bias both the detectors D1and D2 will detect the signal of wavelengths—λ₁ & In the wavelengthmodulation scheme using two LEDs integrated in one device, when LED1 isturned ON detector 1 will pick up the signal of wavelength λ₁ and whenLED2 is turned ON detector 2 will pick up the signal of wavelength λ₂.

The dual-wavelength LED and detector designs can be extended to multiplewavelengths λ₁, λ₂, . . . , λ_(N). In this approach, the LED andcorresponding detectors of FIG. 62 and FIG. 63. will have multiplequantum wells QW₁, QW₂, . . . , QW_(N) each tuned to the individualwavelengths λ₁, λ₂, . . . , λ_(N).

The TCAD simulated structure of two wavelength InGaAs/GaAsPphotodetector is shown in epitaxial stack diagram 6600 of FIG. 66. Thephotodetector is a three terminal device. Two devices with two sets ofInGaAs QWs of different Indium composition are stacked on top of eachother. The n+ contact is shared by the two devices. The photodetectorwith InGaAs QWs of lower Indium percentage is stacked on top of thephotodetector with InGaAs QWs of higher Indium composition. This allowsthe (higher wavelength) light to be detected by the lower QWs to passthrough the upper QW layers. The p+ contact layer of the photodetectorwith InGaAs QWs of lower Indium composition is at the top of thestructure, the InGaAs QWs are stacked below the p layers, the InGaAs QWswith higher Indium composition are stacked below the n+ contact layerwhich is shared by the two devices. The p+ contact layer for thephotodetector with InGaAs QWs of higher Indium composition is at thebottom of the device as shown in the FIG. 66. Light is incident at thetop device surface. The light of higher wavelength will pass through theupper QWs and will generate photo-carriers in the lower QWs, and currentwill be detected at the bottom (anode) electrode. Both the upper andlower QWs will generate carriers when light of lower wavelength is shoneon the device, and current will be detected at both the upper and lower(anode) electrodes.

Graph 6700 of FIG. 67 illustrates the absorption spectrum of thephotodetector when the light with the emission spectrum at 1.6 V of thesingle QW InGaAs/GaAsP LED with 30% Indium and 45% P is incident on thephotodetector. At 1.6 V, the peak emission wavelength is 1070 nm Minimumabsorption will take place in the upper QW layers with 10% Indiumcomposition and most of the light (spectrum at 1.6 V) will be absorbedto generate photo current in the lower QWs with 23% Indium compositionas indicated in graph 5800 of FIG. 58. The peak emission wavelength at1.8 V of the single QW InGaAs/GaAsP LED with 30% Indium and 45% P is 917nm. The spectrum of light at 1.8 V will be absorbed by both the upperand lower QWs and photo current will be detected in both the upper andlower (anode) electrodes as shown in graph 6900 of FIG. 69. Thetransient response of the photodetector for incident light with peakemission wavelength of 1070 nm is also shown in FIG. 69.

In certain embodiments, the previously disclosed epitaxial structuresmay have stated material compositions having a variance of +/−10% andstated dimensions having a variance of +/−10%. In other embodiments, thepreviously disclosed structures may have stated material compositionshaving a variance of +/−5% and stated dimensions having a variance of+/−5%

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” As used herein, the terms “connected,”“coupled,” or any variant thereof, means any connection or coupling,either direct or indirect, between two or more elements; the coupling ofconnection between the elements can be physical, logical, or acombination thereof. Additionally, the words “herein,” “above,” “below,”and words of similar import, when used in this application, shall referto this application as a whole and not to any particular portions ofthis application. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number respectively. The word “or,” in reference to alist of two or more items, covers all of the following interpretationsof the word: any of the items in the list, all of the items in the list,and any combination of the items in the list.

The above detailed description of embodiments of the disclosure is notintended to be exhaustive or to limit the teachings to the precise formdisclosed above. While specific embodiments of, and examples for, thedisclosure are described above for illustrative purposes, variousequivalent modifications are possible within the scope of thedisclosure, as those skilled in the relevant art will recognize. Forexample, while processes or blocks are presented in a given order,alternative embodiments may perform routines having steps, or employsystems having blocks, in a different order, and some processes orblocks may be deleted, moved, added, subdivided, combined, and/ormodified to provide alternative or sub-combinations. Each of theseprocesses or blocks may be implemented in a variety of different ways.Also, while processes or blocks are at times shown as being performed inseries, these processes or blocks may instead be performed in parallel,or may be performed at different times. Further any specific numbersnoted herein are only examples: alternative implementations may employdiffering values or ranges.

The teachings of the disclosure provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

Any patents and applications and other references noted above, includingany that may be listed in accompanying filing papers, are incorporatedherein by reference. Aspects of the disclosure can be modified, ifnecessary, to employ the systems, functions, and concepts of the variousreferences described above to provide yet further embodiments of thedisclosure.

These and other changes can be made to the disclosure in light of theabove Detailed Description. While the above description describescertain embodiments of the disclosure, and describes the best modecontemplated, no matter how detailed the above appears in text, theteachings can be practiced in many ways. Details of the system may varyconsiderably in its implementation details, while still beingencompassed by the subject matter disclosed herein. As noted above,particular terminology used when describing certain features or aspectsof the disclosure should not be taken to imply that the terminology isbeing redefined herein to be restricted to any specific characteristics,features, or aspects of the disclosure with which that terminology isassociated. In general, the terms used in the following claims shouldnot be construed to limit the disclosure to the specific embodimentsdisclosed in the specification, unless the above Detailed Descriptionsection explicitly defines such terms. Accordingly, the actual scope ofthe disclosure encompasses not only the disclosed embodiments, but alsoall equivalent ways of practicing or implementing the disclosure underthe claims.

The invention claimed is:
 1. A free space optical (FSO) communicationapparatus, comprising: a input digital data port; deserializer circuitryelectrically coupled with the input digital data port; first currentdrive circuitry electrically coupled with the deserializer circuitry;second current drive circuitry electrically coupled with thedeserializer circuitry; a first epitaxial structure electrically coupledwith the first current drive circuitry, wherein: the first epitaxialstructure is configured to receive a first bias voltage; and the firstepitaxial structure comprises a first optical source configured to: tohave a transient response time of at least less than 500 picoseconds;and transmit at a first wavelength, wherein the first wavelength isbased at least partially on the first bias voltage; and a secondepitaxial structure electrically coupled with the second current drivecircuitry, wherein: the second epitaxial structure is configured toreceive a second bias voltage; and the second epitaxial structurecomprises a second optical source configured to: to have a transientresponse time of less at least less than 500 picoseconds; and transmitat a second wavelength, wherein the second wavelength is based at leastpartially on the second bias voltage, wherein the first wavelength andthe second wavelength are mutually exclusive.
 2. The FSO communicationapparatus of claim 1, wherein the first epitaxial structure furthercomprises: a substrate; and a carrier confinement (CC) region positionedover the substrate, the CC region defining: a first CC layer comprisingat least one of indium gallium phosphide, aluminum gallium arsenide,aluminum gallium nitride, or aluminum gallium antimonide; and a secondCC layer positioned over the first CC layer, the second CC layercomprising at least one of gallium arsenide phosphide, aluminum galliumarsenide, aluminum gallium nitride, or aluminum gallium antimonide. 3.The FSO communication apparatus of claim 1, wherein the first epitaxialstructure is implemented within a flip-chip package.
 4. The FSOcommunication apparatus of claim 1, wherein the input digital data portis electrically coupled with a high speed computer interface port. 5.The FSO communication apparatus of claim 4, wherein the high speedcomputer interface port is compliant with at least one of a UniversalSerial Bus (USB) interface port, a Serial ATA (SATA) interface port, andan Ethernet interface port.
 6. The FSO communication apparatus of claim4, wherein the high speed computer interface port is compliant withUniversal Serial Bus (USB) Type-C connector (USB-C) interface.
 7. TheFSO communication apparatus of claim 1, wherein the input digital dataport is electrically coupled with at least one of a gigabit interfaceconverter (GBIC) interface interfact port, a small form-factor pluggable(SFP) interface port and a 10 Gigabit Small Form Factor Pluggable (XFP)interface port.
 8. The FSO communication apparatus of claim 1, whereinthe input digital data port is electrically coupled with a high speedaudio/video interface port.
 9. The FSO communication apparatus of claim8, wherein the high speed audio/video interface port is compliant withis compliant with at least one of a High-Definition Multimedia Interface(HDMI) port, a DisplayPort interface port, and a Digital VisualInterface (DVI) port.
 10. The FSO communication apparatus of claim 1,wherein the first epitaxial structure is a light-emitting-diode (LED).11. A free space optical (FSO) communication apparatus, comprising: anoutput digital data port; serializer circuitry electrically coupled withthe output digital data port; first transimpedance amplifier circuitryelectrically coupled with the serializer circuitry; secondtransimpedance amplifier circuitry electrically coupled with theserializer circuitry; a first epitaxial structure electrically coupledwith the first transimpedance amplifier circuitry, wherein: the firstepitaxial structure is configured to receive a first bias voltage; andthe first epitaxial structure comprises a first optical detectorconfigured to: to have a transient response time of at least less than500 picoseconds; and receive at a first wavelength, wherein the firstwavelength is based at least partially on the first bias voltage; and asecond epitaxial structure electrically coupled with the secondtransimpedance amplifier circuitry, wherein: the second epitaxialstructure is configured to receive a second bias voltage; and the secondepitaxial structure comprises a second optical detector configured to:to have a transient response time of at least less than 500 picoseconds;and receive at a second wavelength, wherein the second wavelength isbased at least partially on the second bias voltage, wherein the firstwavelength and the second wavelength are mutually exclusive.
 12. The FSOcommunication apparatus of claim 11, wherein the first epitaxialstructure further comprises: a substrate; and a carrier confinement (CC)region positioned over the substrate, the CC region defining: a first CClayer comprising at least one of indium gallium phosphide, aluminumgallium arsenide, aluminum gallium nitride, or aluminum galliumantimonide; and a second CC layer positioned over the first CC layer,the second CC layer comprising at least one of gallium arsenidephosphide, aluminum gallium arsenide, aluminum gallium nitride, oraluminum gallium antimonide.
 13. The FSO communication apparatus ofclaim 11, wherein the first epitaxial structure is implemented within aflip-chip package.
 14. The FSO communication apparatus of claim 11,wherein the output digital data port is electrically coupled with a highspeed computer interface port.
 15. The FSO communication apparatus ofclaim 14, wherein the high speed computer interface port is compliantwith at least one of a Universal Serial Bus (USB) interface port, aSerial ATA (SATA) interface port, and an Ethernet interface port. 16.The FSO communication apparatus of claim 14, wherein the high speedcomputer interface port is compliant with Universal Serial Bus (USB)Type-C connector (USB-C) interface.
 17. The FSO communication apparatusof claim 11, wherein the output digital data port is electricallycoupled with at least one of a gigabit interface converter (GBIC)interface interfact port, a small form-factor pluggable (SFP) interfaceport and a 10 Gigabit Small Form Factor Pluggable (XFP) interface port.18. The FSO communication apparatus of claim 11, wherein the outputdigital data port is electrically coupled with a high speed audio/videointerface port.
 19. The FSO communication apparatus of claim 18, whereinthe high speed audio/video interface port is compliant with is compliantwith at least one of a High-Definition Multimedia Interface (HDMI) port,a DisplayPort interface port, and a Digital Visual Interface (DVI) port.20. A free space optical (FSO) communication apparatus, comprising: aninput digital data port; deserializer circuitry electrically coupledwith the input digital data port; first current drive circuitryelectrically coupled with the deserializer circuitry; second currentdrive circuitry electrically coupled with the deserializer circuitry; afirst epitaxial structure electrically coupled with the first currentdrive circuitry, wherein: the first epitaxial structure is configured toreceive a first bias voltage; and the first epitaxial structurecomprises a first optical source configured to: to have a transientresponse time of at least less than 500 picoseconds; and transmit at afirst wavelength, wherein the first wavelength is based at leastpartially on the first bias voltage; a second epitaxial structureelectrically coupled with the second current drive circuitry, wherein:the second epitaxial structure is configured to receive a second biasvoltage; and the second epitaxial structure comprises a second opticalsource configured to: to have a transient response time of less at leastless than 500 picoseconds; and transmit at a second wavelength, whereinthe second wavelength is based at least partially on the second biasvoltage. an output digital data port; serializer circuitry electricallycoupled with the output digital data port; first transimpedanceamplifier circuitry electrically coupled with the serializer circuitry;second transimpedance amplifier circuitry electrically coupled with theserializer circuitry; a third epitaxial structure electrically coupledwith the first transimpedance amplifier circuitry, wherein: the thirdepitaxial structure is configured to receive a third bias voltage; andthe third epitaxial structure comprises a first optical detectorconfigured to: to have a transient response time of at least less than500 picoseconds; and receive at a third wavelength, wherein the firstthird wavelength is based at least partially on the third bias voltage;and a fourth epitaxial structure electrically coupled with the secondtransimpedance amplifier circuitry, wherein: the fourth epitaxialstructure is configured to receive a fourth bias voltage; and the fourthepitaxial structure comprises a second optical detector configured to:to have a transient response time of at least less than 500 picoseconds;and receive at a fourth wavelength, wherein the fourth wavelength isbased at least partially on the fourth bias voltage, wherein the firstwavelength, the second wavelength, the third wavelength, and the fourthwavelength are all mutually exclusive.